Aquaporin Water Channels in Central Nervous System

Aquaporins (AQPs) are a family of water-selective channels that provide a major pathway for osmotically driven water transport through cell membranes. Some members of the aquaporin family have been identified in the central nervous system (CNS). The water channel aquaporin 1 (AQP1) is restricted to the apical domain of the choroid plexus epithelial cells. The AQP4 is abundantly expressed in astrocyte foot processes and ependymocytes facing capillaries and brain-cerebrospinal fluid (CSF) interfaces, whereas AQP9 is localized in tanycytes and astrocytes processes. The mRNA for other aquaporin homologs (i.e., AQP3, 5, and 8) have been recently found in cultured astrocytes. Based on their subcellular localization and data obtained from functional studies, it is assumed that aquaporins are implicated in water movements in nervous tissue and may play a role in central osmoreception, K+ siphoning, and cerebrospinal fluid formation. There have been recent reports describing different aquaporin-responses under pathologic states leading to brain edema. The data available provide a better understanding of the mechanisms responsible for brain edema and indicate that aquaporins are potential targets for drug development.